Pulse reflecting highway signalling system

ABSTRACT

A signaling system designed primarily for use on limited access highways. A plurality of individual stations positioned along the right of way of a highway are connected to a master control by a coaxial cable. Each individual station consists of a means for varying the impedance of the coaxial cable to one of a selected number of different impedances including for example an open circuit, a short circuit, a partial open circuit and a partial short circuit. The stations of each are located at different distances along the length of the cable as for example every tenth of a mile. The cable is constantly monitored from the master control by pulse signals. Reflections of the pulse signals are displayed on an oscilloscope which is calibrated for an A scope visual display and indication of the particular station from which a pulse signal is reflected or partially reflected by an impedance mismatch. In a modification, in place of a coaxial cable with individual stations there is provided a parallel pair of normally spaced wires supported by a dielectric whereby the conductive wires may be moved toward one another to change the characteristic impedance at a given location.

United States Patent Wolf [54] PULSE REFLECTING HIGHWAY SIGNALLING SYSTEM [72] Inventor: David Wolf, 67 Brackett Road,

Newton, Mass. 02158 [22] Filed: Aug. 10, 1970 [21] Appl. No.: 62,417

Related us. Application Data [63] Continuation-in-part of Ser. No. 29,122, April 16, 1970, abandoned.

[52] US. Cl ..340/22, 324/52 [51] Int. Cl. ..G01r 31/11 [58] Field of Search ..340/22, 23, 31 R, 32, 33, 34,

[56] References Cited I UNITED STATES PATENTS 3,600,674 8/1971 Roberts et al. ..324/52 3,434,049 3/1969 Frye "324/52 3,477,019 11/1969 I-Iartmann ..324/52 2,974,304 3/ 1961 Nordlund ..340/22 3,283,297 11/1966 Pfennighausen et al.....340/22 3,471,649 10/1969 Carle ..l79/81 3,517,306 6/1970 Anderson et al. ..l79/175.3

OTHER PUBLICATIONS Harley Halverson, Testing Microwave Transmission Lines, Electronics, June 30, 1961, pages 86- 89.

[451 Se t. 12, 1972 [5 7] ABSTRACT A signaling system designed primarily for use on limited access highways. A plurality of individual stations positioned along the right of way of a highway are connected to a master control by a coaxial cable. Each individual station consists of a means for varying the impedance of the coaxial cable to one of a selected number of different impedances including for example an open circuit, a short circuit, a partial open circuit and a partial short circuit. The stations of each are located at different distances along the length of the cable as for example every tenth of a mile. The cable is constantly monitored from the master control by pulse signals. Reflections of the pulse signals are displayed on an oscilloscope which is calibrated for an A scope visual display and indication of the particular station from which a pulse signal is reflected or partially reflected by an impedance mismatch. In a modification, in place of a coaxial cable with individual stations there is provided a parallel pair of normally spaced wires supported by a dielectric whereby the conductive wires may be moved toward one another to change the characteristic impedance at a given location.

19 Claims, 7 Drawing Figures PATENTED SEP 12 m2 SHEET 1 BF 2 L 1 $5? K X U l bi j \PNF m m mmwmw WNW WWW m r. E B, UR m Whig Z ZJM PULSE REFLECTING HIGHWAY SIGNALLING SYSTEM RELATED CASES This is a continuation in part of application Ser. No. 29,122 filed Apr. 16, 1970, now abandoned.

SUBJECT MATTER OF THE INVENTION The present invention relates to a signaling system and is particularly designed as a signaling system for highway safety purposes.

BACKGROUND OF THE INVENTION For some time there has been a need to provide an improved means by which a motorist on an open highway can call for assistance. Various solutions have been proposed. These include, for example, a highway signaling system having a series of wireless transmitters located along the highway. A motorist in distress would suitably actuate one of these transmitters which in turn would generate a signal in a central receiver at some remote point. In another system, conventional telephone communication means are used. Such systems are frequently found on bridges and on some limited access highways. These and other proposed systems have various limitations which have precluded their universal use. These limitations include, for example, problems of transmission interferences in the case of wireless systems from nature and other operating communication devices. In addition, these prior art systems are expensive, difficult to maintain, highly susceptable to vandalism, not easily monitored, and often require significant supervision. In addition, the satellite of signaling stations are too complicated and expensive to permit adaptation of the system to varying conditions and situations.

SUMMARY OF THE INVENTION The present invention provides an improved highway signaling system which does not have the limitations of many presently existing and conceived signaling systems. In. the present invention there is provided means by which a motorist in distress may signal a central station of his location and the nature of his distress from any one of a number of simple inexpensive stations that extend the length of the highway.

It is an object of the present invention to provide a highway signaling system in which a number of signaling stations are located along the length of a highway at any desirable convenient distance. Each of these stations provides an electrical circuit capable of actuating a signal at a master station or console for purposes of indicating the location of the particularstation and one of several different types of distress calls. A controller at the master station may thus determine the nature of assistance needed and the location to which the assistance is to be sent.

It is an object of this invention to provide individual stations which are easily mass produced, are simple and rugged in design, are easily weatherproofed, are not susceptible to vandalism, can be easily replaced without significant expense and are readily connectible to the master control. It is also an object of the present invention to provide an improved highway signaling system in which a master control is connected to any select number of stations along the length of a highway by a cable in which the status and effectiveness of the cable is subject to constant monitoring from the master station. A further object of the present invention is to provide a highway signaling system which is easily adapted for use under a variety of highway conditions for various length highways from a few miles to hundreds of miles and with stations at different locations depending upon the particular requirements of the installation.

In a modification of the invention it is an object of the invention to provide means by which a signal may be generated at any point along a pulse transmission line by hand pressure for purposes of signaling the location of the pressure.

A further object of the present invention is to provide an improved highway signaling system which utilizes a cable, preferably coaxial or parallel line, extending lengthwise of the highway with the cable of uniform impedance characteristics. Means are provided to transmit pulses along the cable and to receive reflected pulse signals from impedance mismatches at discreet positions along the cable. Means are provided for determining the location of the mismatch by determining the time lapse of the reflected pulse signal from the mismatch. In addition, means are provided for determining the amplitude of the reflected signal with respect to other reflections from the same station.

These and other objects and advantages of the present invention will be more clearly understood when considered in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a preferred embodiment of the invention illustrated generally in schematic outline;

FIG. 2 illustrates an elevational view of a typical station used in highway installations;

FIG. 3 illustrates a schematic of an electrical circuit of one embodiment of a station;

FIG. 4 illustrates a face of an oscilloscope in opera tion of a system.

FIG. 5 illustrates a schematic of a modification of the invention,

FIG. 6 is a cross sectional view of the cable used in the modification of FIG. 7. and

FIG. 7 is a schematic illustration of a modification of the invention.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will be described in conjunction with a preferred embodiment for use on a limited access highway. It should be understood, however, that there are other applications for the: present invention in which signaling from remote locations with a limited variety of signals is desired. Such additional applications might, for example, mine installations and installations in patrolled areas such as prison camps, tunnels or bridges.

In the preferred embodiment described in this application, the system is intended for use on a limited access highway such for example as a toll road. Typically the system could be installed along the length of the road between adjacent toll booths approximately 20 miles apart.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, there is illustrated schematically four cables identified as cable A, cable B, cable C and cable D. Cables A and B extend lengthwise down a limited access highway on opposite sides of the highway in one direction from a master station 1. Cables C and D extend down the highway also on opposite sides in the direction opposite to the direction which cables A and B extend. The highway may comprise a conventional limited access highway such as a toll road. The central control 1 may be located in a suitable location as for example a police station on the highway or in the office of the toll station. In the absence of such a station on the highway being monitored, the cables A, B, C and D may be connected to a remote station by suitable means, such for example as a leased telephone line. In the specific illustration described, the cables extend a length of approximately 20 miles each. They need not however all extend to equal lengths, but are obviously adaptable to the particular requirements of the system. Thus, for example, other systems may be provided in series at the ends of the specific system illustrated in FIG. I to provide a continuous monitored system along extended lengths of a highway. Cable A and cable D may be one side of the right way as for example on the south side of the highway while cables B and C may be on the north side of the right of way. In some systems a single cable may extend along the right of way. In another system a single master station may have a plurality of cables that extend on the same side of a road to different distances as shown schematically in FIG. 4.

"The cables are suitably secured along the highway either underground or above ground or a combination of both depending upon the nature of the installation. The cables should be conventional weatherproof cables capable of withstanding normal exposure for prolonged periods of time. Each cable comprises preferably a coaxial line having a uniform characteristics impedance preferably in the order of between 50 and 500 ohms.

Each cable is provided with a series of stations preferably identical in nature and spaced at convenient but not necessarily uniform distances apart. These stations, as for example in cable A, are identified as stations 1A, 2A, 3A, 4A, 5A NA. The stations may for example be located approximately 500 to 1,000 feet apart depending upon the needs of the specific installation. Preferably the station should be close enough so that a motorist in distress can walk from a car along the highway to a station within a short period of time. Preferably the station should be visible from one station to the next so as to provide a convenient means for signaling purposes. The stations in the other cables are similar in nature and are identified respectively in cable B at 1B, 2B, 3B, 4B, 5B NB; in cable C at 1C, 2C, 3C, 4C, 5C NC; and in cable D at 1D, 2D, 3D, 4D, 5D ND.

A pulse generating circuit 2 within the station 1 is electrically sequentially connected to each of the cables A, B, C, and D for sequential firing. This pulse generating circuit may be of conventional design and capable of pulsing each cable. The pulse which the circuit 2 must be capable of generating may vary depending upon the specific applications involved. However, it is preferable that the pulses be of low average power but of high peak power having a rectangular shape and an amplitude of several thousand of volts with a duration of in the order of to 500 nanoseconds and with a pulse repetition frequency of up to several hundreds or thousands cycles per second. The lower limits of the voltage are determined by the attenuation factors of the cable. The minimum repetition frequency is determined by the persistence of vision and brightness factor of the CRT display described below. A suitable pulse generator of the type required is made by Tobe Deutschmann Laboratories of Canton, Massachusetts, and is sold under the trademark Telemetroscope". If desired, separate pulse generating circuits may be used for each of the cables instead of a circuit for sequentially scanning the cables from the same pulse generating circuit as described above.

One end of each cable is impedance matched to terminals of the pulse generating circuit. The other ends of each cable is preferably terminated by an impedance mismatch. An open circuit mismatch is preferred.

The cables A, B, C and D are preferably coaxial cables illustrated in greater schematic detail in FIG. 3 which also shows a typical station as for example station 2A. The leads 5 and 6 of the coaxial cable are connected to a series arrangement of switches 7, 8, 9 and 10 at each station. Preferably, one of the leads, for example, lead 6 forms a ground loop. Switch 7 is a normally closed switch that may be thrown from terminal 11 in series with lead 5 to terminal 12 that is connected to lead 5 through a resistor 13. In a 500 ohm cable resistor 13 may have a value in the order of 750 ohms. When the switch 7 is open to terminal the coaxial cable is effectively thereby partially opened.

In series with switch 7 is normally closed switch 8. This switch 8 may be thrown from its normally closed position at terminal 14 to terminal 15 to fully open the cable. Switch 9 in series with switch 8 is a normally opened switch which may be thrown from its normally opened position at terminal 16 to terminal 17 which is connected to lead 6 through resistor 18. Resistor 18 may have a value in the order of 250 ohms in a 500 ohm coaxial cable. When the switch is connected to terminal 17 the cable is effectively partially shorted. Switch 10 is a normally open switch that may be thrown from its normally open position at terminal 9 in series with switch 9 to terminal 20 connected directly to lead 6. When thrown to terminal 20 the cable is effectively shorted.

The stations are each provided with suitable instructions depending upon the nature of the use of the system. In a typical limited access highway, the stations may be provided with nomenclature, as illustrated if FIG. 2, that identifies each switch or button control. For example, switch 7 illustrated in FIG. 3 may be controlled by button 31 which is labelled out of gas. Thus a motorist will push button 31 to generate an out of gas signal. Similarly, button 32 which controls switch 8 may be pushed to generate a breakdown condition; button 33, which controls switch 9 may be pushed to generate a collision" condition; and button 34 which controls switch 10 may be pushed to generate a serious collision" condition.

The stations each may comprise a suitable weatherproofed housing 30 preferably made of metal with the circuitry appropriately contained within and to the extent possible properly potted. The buttons 31 to 34 project through the face of the housing 30 adjacent the appropriate identifying language.

The buttons are preferably of the momentary variety in which the switches they control are only momentarily closed regardless of the time period that the button is depressed. This momentary arrangement is preferred to avoid or minimize the likelihood of a blocking signal. Such blocking signal would, for example, occur if a remote signal is generated while the cable is open as a result of a signal from a station closer to the central control. Under these conditions the signal generated at a station closer to the central control may block a signal from the more remote station.

These stations are suitably supported along the highway, as for example, on tubular stanchions or perhaps on tenth mile marker posts.

At the control station there is provided a receiver 40 having a visual CRT display upon which reflected signals are displayed. In the arrangement described, four signals may be displayed in an A scope presentation. A conventional oscilliscope display may be used in which an input signal is suitably amplified by known means and displayed on the scope. Preferably the amplifier in the receiver has a time dependant gain control to compensate for normal attenuation of remote signals. These displays correspond to and are appropriately labelled for each of the cables A, B, C and D. The time scale for these displays may be calibrated in distance or two way travel time. Thus, for example, if the cables extend a distance of twenty miles each the lines from one end 30 to the other end 31 are calibrated to indicate a distance of 20 miles by scale 32. The scale 32 may also be calibrated and marked to identify the relative location along the length of the displayed distance the location of individual stations. This may be done by marking the relevant position by numbers 33 corresponding in relative location to the location of the stations along the highway. The scale indicates the amplitude of the reflected signal. The Y scale need be scaled only to indicate whether the reflected pulse signal is from a partial or completely open or shorted line. In the embodiment illustrated, each reflected signal on the CRT shows a full impedance mismatch at the end of the cable at 31. This is desirable for calibration purposes on both the X and Y axis. As illustrated a signal has been generated at station 3 on cable D as indicated at 33. This is a full scale deflection indicating a fully shorted station and consequently a signal on button 34 of station 3D which in turn indicates a serious accident. At the same time a partial short is also being shown at 34 indicating a partial shorted station and consequently a signal on button 33 of station 3C which I If desired, an arrangement as illustrated in FIG. 5 may be used. Here two cables E and F having stations 1E to NF and IF to NF similar in arrangement to those previously described are connected to the cables. The cable F however extends along the same side of the highway as cable E but extends for a considerably greater distance. Thus, for example, cable E extends a distance of 20 miles and cable F extends 40 miles. The stations IE to NE are connected to cable E at appropriate distances as previously described. The stations IE to NF on the other hand are connected to cable F only along the length of the cable from a point at which cable E ends to the remote end of cable F. This array permits a better display on the CRT of signals from the cables as it permits a spreading on the X axis of the signals along the 40 miles of highway.

Referring now to FIGS. 6 and 7 there is shown a modification of the invention in which the system includes a pulse generator and a receiver including an amplifier 101 and suitable display means such as a conventional video display 102 all similar to those previously described. These components are connected to the line 103 so that the characteristic impedance of line 103 is properly matched and pulses generated down the line by the generator 100 and reflected by introduced mismatches may be displayed as described above on the video display 102.

The line 103 extends above ground 105 along major portions but may where convenient and where access to it is not desired extend below ground as for example at 106. This portion may for example be in an area where the line extends across an intersection. The line 103 should preferably be supported for easy access by people in distress. Thus the line 106 may extend lengthwise of the road, or perhaps a bridge or other area being monitored. If on a road it would be in the right of way or off the edge of the road. If on a bridge it may be supported on a railing. The line preferably should be several feet off the ground, as for example, three feet for easy access by individuals.

If the line is supported above ground suitable supports 107 may be provided. These supports may comprise a metal post 108 buried at its lower end in the ground. The upper end of the support is provided with a clamp 109 having a hinged opening 110 to permit insertion of the line 103. A sign 111 containing suitable instructions may be integrally formed on the support.

The line 103 is illustrated in cross section in FIG. 6. The line 103 includes a pair of conductive wires I12 and 113 that extend the length of the line and are suitably connected to the generator and receiver with one wire acting as ground with respect to the other. The wires 112 and 113 are suitably supported in a dielectric casing 114 which is preferably hollow providing an air coredielectric 115. The casing 114 may be of any suitable weather resistant waterproof resilient deformable material. Materials such as polypropylene or other known plastics capable of providing the described functions are suitable. The casing supports the wires 112 and 113 in normal spaced relation with the characteristic impedance as for example 300 ohms, at least in part determined by the distance between the wires. Preferably the wires are supported with portions 116 extending their length free of any covering. These portions 116 should be opposed to each other. The

plastic casing should be such as to permit compression of the line by hand pressure of several pounds whereby the wires 112 and 113 may be moved toward one another into touching relation at the portions 116 immediately under the hand pressure. This action will change the characteristic impedance of the line and will cause mismatches at that particular point. Release of the hand pressing will allow return of the wires to their normal spaced position.

The casing 114 may be thicker on portions bordering the wires and thinner at points intermediate as illustrated respectively at 117 and 118. This will assure closing of the wires into contact with one another at the point of hand compression.

In the operation of this embodiment a distressed motorist will simply walk from his car to the line 103 and squeeze it as directed.

The wire may be squeezed multiple numbers of times to give different signals. For example one squeeze for out of gas and two squeezes for an accident. The pulses being generated will be appropriately reflected and may be read as previously described.

This modification of the invention is particularly useful in areas where it is desirable to minimize movement of a person. For example it is not desirable to permit movement of people on bridges or tunnels having limited or no sidewalks. The modification provides a line which may be reached by a motorist without leaving the immediate area of his car. The system may also be used in other areas and under other conditions in which remote location and quality signaling is desired.

In the modification of FIG. 6 the line may instead of being oval in cross sectional shape as illustrated may take other forms such as circular. It is also possible that the inner surface of the cable may be coated with strips of conductive material instead of being provided with wires.

The standards or supports are intended to be constructed to adequately support the line. In this connection it is contemplated that the line may be clipped to guide rails.

The system also contemplates a combination of the embodiments disclosed. Thus on a super highway that has a series of bridges or tunnels, the embodiment of FIGS. 1 to 4 may be used on the open highway and the embodiment of FIGS. 5 and 6 may be used on the bridges and tunnels.

The receiver disclosed may be a remote receiver if there is no facility near the highway being monitored. In such arrangements a suitable amplifier and transmitter which require no constant monitoring would be provided adjacent the line near the highway. This transmitter would be connected by conventional telephone cable techniques to a remote receiver which, for example may be housed in a remote police station. The displays would be similar to those previously described but would be at a remote distance. Such a central monitoring station might be used to control a plurality of such systems.

Iclaim:

1. Signalling system comprising an electrically conductive cable having a first impedance characteristic, means for impressing pulse signals on the cable to cause said pulse signals to propagate along the length of said cable, means for receiving reflection of said pulse signals from impedance mismatches along said cable and for displaying said reflections including means for discriminating between reflections of different magnitudes and reflections from different locations along said cable, and a plurality of mismatch-producing means spaced along and each electrically connected to said cable, said mismatch-producing means each being adapted to selectively cause any one of a plurality of different impedance mismatches of different magnitudes.

2. A signaling system as set forth in claim 1 for highway signaling including said cable extending lengthwise along said highway at least a distance in the order of a mile, and said means for impressing pulse signals including means for impressing a plurality of signals of like characteristics for continued sampling and monitoring of said cable.

3. A signalling system as set forth in claim 2 wherein said mismatch-producing means each include means for creating an impedance mismatch which is different from the impedance mismatch caused by an open circuit in said cable.

4. A signaling system as set forth in claim 2 wherein said mismatch-producing means comprises a plurality of switches electrically connected in said cable for selectively switching different impedance mismatches into said cable.

5. A signaling system as set forth in claim 4 wherein said mismatch-producing means each include a plurality of different resistances for connection by said switch means to said cable.

6. A signaling system as set forth in claim 2 wherein said cable comprises a coaxial cable.

7. A signaling system as set forth in claim 6 wherein said mismatch-producing means each includes a plurality of resistances of different magnitudes and means for selectively mismatching the impedance at said mismatch-producing means.

8. A signalling system as set forth in claim 2 wherein said mismatch-producing means each includes means for creating an impedance mismatch which is different from the impedance mismatch caused by a closed circuit in said cable.

9. In a signaling system for signaling along highway bridges and the like, pulse emitting means, a line normally having a uniform characteristic impedance along its length and along which pulses from said pulse emitting means may be propagated, pulse receiving means for receiving pulses reflected by aberrations in said uniform characteristic impedance at discrete points along said line, normally said line including at least one pair of conductive elements spaced at uniform distances apart at least in part defining said characteristic impedance and means supporting said elements capable of being manually moved toward and away from one another for movement toward and away from one another at discrete positions along the length thereof to create aberrations in said uniform characteristic impedance for reflecting pulses to said means for receiving pulses whereby the distance between the aberrations and the pulse receiving means may be determined.

10. In a system as defined in claim 9 said line including said support means comprising a dielectric material supporting said conductive elements along their length with said dielectric material of sufficient flexibility to permit said conductive elements to be moved toward and away from one another.

11. In a system as set forth in claim 9 said line including said support means comprising an elongated dielectric material supporting said wires in normal uniform spaced relation along their length, said dielectric material comprising a material that may be flexed under application of local pressure in the order of mag nitude of several pounds whereby said wires may be moved by application of such pressures at opposed portions of said line at a localized point toward one another whereby the characteristic impedance of said line at said localized point may be varied, said dielectric material also having a resiliency sufficient to permit return of said wires to their original spaced relation upon release of said pressures.

12. A system as set forth in claim 11 wherein said support means comprises a tubular dielectric member and said wires extend lengthwise thereof on the interior of said dielectric member in spaced facing relation.

13. A system as set forth in claim 12 wherein said wires are each formed with one circumferential portion supported by the interior of said tubular member.

14. A system as set forth in claim 13 wherein said tubular member is of non-uniform thickness.

15. A system as set forth in claim 13 including a plurality of vertical standards supporting said line above ground.

16. A system as set forth in claim 9 with said support means permitting introduction of an abrupt impedance discontinuity in said line in response to an applied pressure and return to said original characteristic impedance upon removal of said applied pressure.

17. A signalling system as set forth in claim 9 wherein said conductive elements and said means supportin said elements comprise a switch.

18. A method of highway signalling comprising propagating electronic pulses along cable means extending lengthwise of a highway from a first point, switching an impedance mismatch into said cable to reflect said pulses from a second one of a plurality of fixed and spaced points and measuring the time of propagation and reflection from the propagating point and determining from said time of propagation and reflection the distance between said first and second points.

19. A method as set forth in claim 18 including selecting one of several impedance mismatches each for reflecting pulses of respectively different characteristics that are indicative of different preselected messages, and determining which one characteristic of said reflected pulses at said first point was reflected to determine said preselected message. 

1. Signalling system comprising an electrically conductive cable having a first impedance characteristic, means for impressing pulse signals on the cable to cause said pulse signals to propagate along the length of said cable, means for receiving reflection of said pulse signals from impedance mismatches along said cable and for displaying said reflections including means for discriminating between reflections of different magnitudes and reflections from different locations along said cable, and a plurality of mismatch-producing means spaced along and each electrically connected to said cable, said mismatch-producing means each being adapted to selectively cause any one of a plurality of different impedance mismatches of different magnitudes.
 2. A signaling system as set forth in claim 1 for highway signaling including said cable extending lengthwise along said highway at least a distance in the order of a mile, and said means for impressing pulse signals including means for impressing a plurality of signals of like characteristics for continued sampling and monitoring of said cable.
 3. A signalling system as set forth in claim 2 wherein said mismatch-producing means each include means for creating an impedance mismatch which is different from the impedance mismatch caused by an open circuit in said cable.
 4. A signaling system as set forth in claim 2 wherein said mismatch-producing means comprises a plurality of switches electrically connected in said cable for selectively switching different impedance mismatches into said cable.
 5. A signaling system as set forth in claim 4 wherein said mismatch-producing means each include a plurality of different resistances for connection by said switch means to said cable.
 6. A signaling system as set forth in claim 2 wherein said cable comprises a coaxial cable.
 7. A signaling system as set forth in claim 6 wherein said mismatch-producing means each includes a plurality of resistances of different magnitudes and means for selectively mismatching the impedance at said mismatch-producing means.
 8. A signalling system as set forth in claim 2 wherein said mismatch-producing means each includes means for creating an impedance mismatch which is different from the impedance mismatch caused by a closed circuit in said cable.
 9. In a signaling system for signaling along highway bridges and the like, pulse emitting means, a line normally having a uniform characteristic impedance along its length and along which pulses from said pulse emitting means may be propagated, pulse receiving means for receiving pulses reflected by aberrations in said uniform characteristic impedance at discrete points along said line, normally said line including at least one pair of conductive elements spaced at uniform distances apart at least in part defining said characteristic impedance and means supporting said elements capable of being manually moved toward and away from one another for movement toward and away from one another at discrete positions along the length thereof to create aberrations in said uniform characteristic impedance for reflecting pulses to said means for receiving pulses whereBy the distance between the aberrations and the pulse receiving means may be determined.
 10. In a system as defined in claim 9 said line including said support means comprising a dielectric material supporting said conductive elements along their length with said dielectric material of sufficient flexibility to permit said conductive elements to be moved toward and away from one another.
 11. In a system as set forth in claim 9 said line including said support means comprising an elongated dielectric material supporting said wires in normal uniform spaced relation along their length, said dielectric material comprising a material that may be flexed under application of local pressure in the order of magnitude of several pounds whereby said wires may be moved by application of such pressures at opposed portions of said line at a localized point toward one another whereby the characteristic impedance of said line at said localized point may be varied, said dielectric material also having a resiliency sufficient to permit return of said wires to their original spaced relation upon release of said pressures.
 12. A system as set forth in claim 11 wherein said support means comprises a tubular dielectric member and said wires extend lengthwise thereof on the interior of said dielectric member in spaced facing relation.
 13. A system as set forth in claim 12 wherein said wires are each formed with one circumferential portion supported by the interior of said tubular member.
 14. A system as set forth in claim 13 wherein said tubular member is of non-uniform thickness.
 15. A system as set forth in claim 13 including a plurality of vertical standards supporting said line above ground.
 16. A system as set forth in claim 9 with said support means permitting introduction of an abrupt impedance discontinuity in said line in response to an applied pressure and return to said original characteristic impedance upon removal of said applied pressure.
 17. A signalling system as set forth in claim 9 wherein said conductive elements and said means supporting said elements comprise a switch.
 18. A method of highway signalling comprising propagating electronic pulses along cable means extending lengthwise of a highway from a first point, switching an impedance mismatch into said cable to reflect said pulses from a second one of a plurality of fixed and spaced points and measuring the time of propagation and reflection from the propagating point and determining from said time of propagation and reflection the distance between said first and second points.
 19. A method as set forth in claim 18 including selecting one of several impedance mismatches each for reflecting pulses of respectively different characteristics that are indicative of different preselected messages, and determining which one characteristic of said reflected pulses at said first point was reflected to determine said preselected message. 